The subject matter of the invention is an apparatus for determining the carbon dioxide content of a liquid, especially of a beverage.
It is known to determine the carbon dioxide content of a beverage, such as beer for example, with an apparatus in which an expansion chamber is provided in a housing for receiving the liquid to be measured. This expansion chamber, however, is connected to a liquid inlet-outlet by an inlet-outlet conduit provided with a valve means. It furthermore contains a pressure gauge as well as a temperature gauge, and its volume is variable according to the position of a piston displaceably disposed in it. The apparatus furthermore has a handle whereby the piston can be drawn from a first position in which the volume of the expansion chamber is at a minimum, to a second position in which the volume of the expansion chamber is at a maximum.
The basis of the known apparatus is the fact that, when there is a state of equilibrium between the carbon dioxide content of the liquid contained in the expansion chamber and the carbon dioxide content of a space situated above the liquid, the carbon dioxide gas pressure which establishes itself in this chamber is an index of the carbon dioxide content of the liquid, depending on the temperature of the liquid.
The measuring process is performed in the known apparatus as follows:
The expansion chamber is completely filled through the feed conduit with the liquid to be measured. Then it is closed by the use of the valve means and the piston is drawn by the handle to the second position, such that a carbon dioxide gas-filled chamber forms above the liquid. The establishment of the equilibrium is assisted and accelerated by shaking the apparatus by hand. The pressure that establishes itself is read on the pressure gauge and, on the basis of the temperature, the corresponding carbon dioxide content of the liquid can be calculated or read from tables in a known manner.
The known apparatus has the disadvantage that it is difficult to operate. Several valves or cocks have to be opened by hand and closed again, the piston has to be drawn out by hand, and the apparatus has to be shaken by hand.
Apparatus have also become known in which the establishment of the state of equilibrium is achieved by special mechanical devices (vibration) or electrical devices (electrolysis).
But these apparatus are relatively complicated in operation. Practice has shown that the known apparatus also require relatively large amounts of test liquid, are liable to trouble, and give readings which are not always repeatable.
Furthermore, an apparatus is known for the continuous determination of the carbon dioxide content of a liquid flowing through a conduit (DE-OS No. 2,634,971), in which a partial stream of the liquid is carried by a measuring conduit through a measuring cell in which an outgassing of the liquid constantly takes place, a static liquid pressure measuring means being provided ahead of the measuring cell and a device for measuring the temperature and a device for measuring the outgassing pressure being disposed within the measuring cell. These measuring apparatus emit electrical signals which are continuously delivered to an electronic computer for evaluation and read-out. The outgassing of the liquid is assisted by constructing the inner chamber of the measuring cell as a cylinder, at least in the area of the entrance of the liquid, and the measuring conduit discharges tangentially to the circumferential surface of the cylinder and the discharge of the liquid takes place in the direction of the axis of the cylinder. At or immediately ahead of the entrance aperture the measuring cell has a narrowing of cross section for the purpose of achieving a sufficient pressure gradient.
With this known apparatus very accurate and repeatable measurements can be obtained, though the technical expense is relatively high.